Multifiber Connectorization Techniques for Multicore Optical Fiber Cables

ABSTRACT

Structures and techniques are described relating to the alignment of multicore fibers within a multifiber connector. These structures and techniques include: multicore fibers having a number of different shapes, including, for example, circular, elliptical, D-shaped, double D-shaped, and polygonal; multifiber ferrules, having a plurality of fiber guide holes therein of various shapes; alignment fixtures for aligning multicore fibers within multifiber ferrules; and various multicore fiber alignment techniques.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of co-pending U.S. patentapplication Ser. No. 13/049,794, filed on Mar. 16, 2011, which claimsthe priority benefit of U.S. Provisional Patent Application Ser. No.61/314,165, filed on Mar. 16, 2010.

All of the above applications are owned by the assignee of the presentapplication and are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of fiber optics,and in particular to improved multifiber connectors for multicoreoptical fiber cables.

2. Background Art

The ever increasing demand for high-density, high-speed parallel opticaldata links, for super-computer and data-center applications, has spawnedsignificant interest in passive optical devices designed to facilitatereliable, cost-effective deployment. In multi-channel parallel links forsuper computers and data centers, thousands of optical links, operatingat 1 Gb/s to 10 Gb/s, may be utilized.

In conventional configurations, one-dimensional parallel optical linkstypically utilize a 1×12 multimode linear array of fibers, with eachfiber serving as a separate channel. In this arrangement, the fibers,which are typically on a 250-μm pitch within a ribbon, are terminatedinto a molded multifiber ferrule, such as an MT ferrule. TheMT-terminated fibers are then used to make connections betweenmulti-channel VSCEL and PiN photodetector arrays. For applicationsrequiring a more rugged assembly, jacketed fibers, typically in a ribbonconfiguration, are terminated within MT ferrules that are then placedinside MT-RJ, MPO, MTP™, or MPX Connector Housings, to produce robustpatch cords.

MT ferrules are available in numerous sizes with various hole counts, toaddress a wide range of connector and signal routing applications. Forexample, the mini MT2 and mini MT4 are used in MT-RJ patch cords. TheMT4, MTB, and MT12 are used in one-dimensional array MPO and MPX patchcords.

For even higher densities, manufacturers terminate fibers into 2D-arrayMT16, MT24, MT48, MT60, or MT72 ferrules. However, high-densityconfigurations assembled using standard single-core fibers have provento be extremely expensive to produce, since achieving physical contactbetween all of the fibers, when two connectors are mated, requires veryprecise control of the polishing process to ensure coplanarity(especially in the 72-fiber variant). Also, the molded MT ferrules arevery expensive to produce. The production yields on 2D-array MT ferrulesleads to significantly higher cost, as one hole out of position causes aferrule to be rejected. For instance, if a 72-fiber ferrule has one holethat doesn't meet positional requirements, then the ferrule is discardedeven though there are 71 correctly positioned holes.

In addition, stacking fiber ribbons to produce the ribbon cordages,needed for the 2D configurations, leads to a relatively large, bulky,and expensive package. Also, the flexibility of the ribbon cordage isadversely affected.

SUMMARY OF THE INVENTION

Aspects of the invention are directed to structures and techniquesrelating to the alignment of multicore fibers within a multifiberconnector. These structures and techniques include: multicore fibershaving a number of different shapes, including, for example, circular,elliptical, D-shaped, double D-shaped, and polygonal; multifiberferrules, having a plurality of fiber guide holes therein of variousshapes; alignment fixtures for aligning multicore fibers withinmultifiber ferrules; and various multicore fiber alignment techniques.

One aspect of the invention provides a multicore fiber, comprising aplurality of cores extending longitudinally within a fiber body. Thefiber body includes at least one flat side surface. The plurality ofcores has a cross-sectional geometrical configuration relative to theflat side surface, such that the at least one flat side surfaceidentifies a particular rotational orientation of the plurality ofcores, and such that precise alignment of the at least one flat sidesurface results in a precise rotational alignment of the plurality ofcores.

A further aspect of the invention provides an alignment fixture. Thefixture has a chassis shaped to receive a multifiber ferrule having abody with an endface from which there extends a plurality of multicorefibers each having a flat side surface identifying a particularrotational orientation of each multicore fiber within a respective guidehole in the ferrule body. The chassis includes a base having a cutoutthat is shaped to closely receive the ferrule body and position it suchthat the flat side surfaces of the multicore fibers abut an alignmentsurface within the fixture. The alignment fixture further comprisesfiber alignment means for urging the flat side surfaces of the multicorefibers against the fiber alignment surface against the fiber alignmentsurface, so as to cause each of the multicore fibers to be rotationallyaligned within its respective guide hole.

A further aspect of the invention provides a multifiber ferrule,comprising a ferrule body having a plurality of guide holes therein forguiding a respective plurality of multicore fibers at an end of amultifiber optical fiber cable. The multicore fibers each have at leastone flat side surface identifying a particular rotational orientation ofthe plurality of cores. The ferrule guide holes each have a shapeincluding a flat side surface corresponding to the at least one flatside surface of the multicore fibers, such that alignment of the atleast one flat side surface of each multicore fiber against thecorresponding flat surface within its respective guide hole results in arotational alignment of the plurality of cores.

Another aspect of the invention is directed to a method for aligningmulticore fibers within a multifiber ferrule. An end portion of amulticore fiber cable containing a plurality of multicore fibers isstripped, so as to expose the bare multicore fibers. The exposedmulticore fibers are inserted into a plurality of guide holes definedlongitudinally through a ferrule subassembly. The cores of the fibersare aligned rotationally, in a predetermined orientation, relative tothe ferrule. The multicore fiber is bonded within the ferrule. The fiberis trimmed at a ferrule endface so as to create a plurality of multicorefiber endfaces protruding from the ferrule endface. The multicore fiberendfaces are then polished.

A further aspect of the invention is directed to a method for aligningmulticore fibers within a multifiber ferrule. An end portion of amulticore fiber cable containing a plurality of multicore fibers isstripped, so as to expose the bare optical fibers. The exposed multicorefibers are inserted into a plurality of guide holes definedlongitudinally through a ferrule subassembly. The multicore fibers arebonded within the ferrule. The multicore fibers are trimmed a ferruleendface, so as to create a plurality of multicore fiber endfacesprotruding from the ferrule endface. The multicore fiber endfaces arethen polished.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show, respectively, a cross section photograph anddiagram of an exemplary MCF 10

FIG. 2A shows a tomographic refractive index profile of the 7-core MCFshown in FIGS. 1A and 1B. FIG. 2B shows an image of a hexagonallyarranged VCSEL array that can be used to interface with the outer sixcores of the MCF shown in FIGS. 1A and 1B. FIG. 2C shows an image of atransmitter subassembly, comprising four side-by-side VCSEL arrays ofthe type shown in FIG. 2B.

FIG. 3 shows a perspective view of an exemplary 12-fiber MT ferrule,into which there are terminated twelve 7-core MCFs.

FIG. 4 shows a cross section of the front section of ferrule shown inFIG. 3, through a plane passing through the longitudinal axes of theMCFs.

FIGS. 5 and 6 show perspective views of exemplary D-shaped 7-coremulticore fibers 50, 60 according to aspects of the invention.

FIG. 7 shows a cross section diagram of the D-shaped MCF shown in FIG.5.

FIG. 8 shows a perspective view of the ferrule shown in FIG. 3, intowhich there has been loaded a multi-MCF cable containing a plurality ofindividual MCFs.

FIG. 9 is a diagram illustrating a general technique for providingalignment of fibers within their respective ferrule guide holes.

FIGS. 10A and 10B show a perspective view of an alignment fixtureemploying a “ramp” technique, in accordance with an aspect of theinvention.

FIGS. 11A-D are a series of diagrams illustrating the operation of thealignment fixture shown in FIGS. 10A-10B.

FIGS. 12A-12C show perspective views of an alignment fixture employing a“tapered slot” technique according to a further aspect of the invention.

FIGS. 13A and 13B are a pair of diagrams illustrating the operation ofthe tapered slot technique.

FIGS. 14A and 14B show perspective views of an alignment fixtureemploying a “side-entry slot” technique, according to a further aspectof the invention.

FIG. 15 shows a diagram illustrating the operation of the side-entryslot technique.

FIGS. 16A and 16B show perspective views an alignment fixture employinga “wedge” technique, according to a further aspect of the invention.

FIGS. 17A-17C are a series of diagrams illustrating the operation of thealignment fixture shown in FIGS. 16A and 16B.

FIG. 18 shows a close-up view of an endface of an MT ferrule endfacewith pre-aligned D-shaped holes.

FIG. 19 shows a close-up front view of the endface of the ferrule shownin FIG. 18, with inserted fibers.

FIG. 20 shows perspective views of multicore fibers having polygonalshapes, according to a further aspect of the invention.

FIGS. 21 and 22 show flowcharts of general techniques according toaspects of the invention.

DETAILED DESCRIPTION

The present description of the invention is organized into the followingsections:

-   -   1. Multicore Multifiber Connectors Using Circular Fibers    -   2. Multicore Multifiber Connectors Using D-Shaped Fibers    -   3. Alignment Techniques for D-Shaped Multicore Fibers        -   3.1 Ramp Method        -   3.2 Tapered Slot Method        -   3.3 Slot Method        -   3.4 Wedge Method    -   4. Multifiber Ferrules with D-Shaped Holes and D-Shaped Fibers    -   5. Multicore Multifiber Connectors Using Polygonal Fibers    -   6. Multicore Multifiber Connectors Using Other Fiber Shapes    -   7. General Techniques    -   8. Conclusion

1. MULTICORE MULTIFIBER CONNECTORS USING CIRCULAR FIBERS

To address the shortcomings of the current approach, multicore fibers(MCF), which can be butt-coupled with specially designed 2-dimensionalVCSEL and PiN photo detector arrays to facilitate simultaneoustransmission over several cores, within each fiber, are utilized.

FIGS. 1A and 1B show, respectively, a cross section photograph anddiagram of an exemplary MCF 10, which is described in greater detail inU.S. patent application Ser. No. 13/045,065, which is owned by theassignee of the present application, and which is incorporated herein inits entirety.

MCF 10 comprises seven graded-index cores, produced from sevengraded-index LaserWave fiber core rods using a stack-and-draw process.The cores are arranged in a hexagonal array including a center core 11and six outer cores 12 positioned at the vertices of a regular hexagon13 in a cladding 14. The diameter of each of the cores is 26 μm, and thecore pitch is 39 μm. The cladding diameter is 125 μm and the acrylatedual coating layer (not shown) is 250 μm. These diameters are compatiblewith conventional optical connectivity products, but other claddingdiameters and geometrical configurations are also feasible. It shouldalso be noted that aspects of the invention described herein may also bepracticed with multicore fibers having different types of cores, such asstep-index or single-mode cores.

FIG. 2A shows a tomographic refractive index profile 20 of MCF 10. FIG.2B shows an image of a hexagonally arranged VCSEL array 22 that can beuse to interface with the outer six cores of MCF 10. FIG. 2C shows anexample of four VCSEL arrays 22, each array comprising six VCSELs. Sucha device could be used to transmit through the six outer cores of a7-core multicore fiber. Of course, other core counts and VCSELconfigurations are possible (e.g., 2×2, etc.).

Aspects of the present invention are described with respect to anexemplary multifiber ribbon cable comprising a plurality of individualMCFs arranged side-to-side in a single linear array. However, it will beappreciated that, with suitable modification as required, the describedstructures and techniques may also be practiced with otherconfigurations.

As mentioned above, MCF 10 has an outer diameter that is compatible withalready existing single-core fiber connectivity products. Thus, amulti-MCF cable will be compatible with ferrules and other connectorsdeveloped for single-core multifiber cables. However, as discussedbelow, beyond the issue of fit, there is an issue with respect toachieving a proper rotational alignment of each individual MCF within agiven connectivity device.

FIG. 3 shows a perspective view of an exemplary 12-fiber MT ferrule 30,into which there are terminated twelve 7-core MCFs 31. FIG. 4 shows across section of the front section of ferrule 30, through a planepassing through the longitudinal axes of MCFs 31.

Ferrule 30 comprises a molded plastic body including two block-shapedsections: base 32 and head 33. A plurality of guide holes 40, arrangedside-to-side in a linear array, extends through the ferrule head 33terminating at ferrule endface 34. Guide holes 40 are shaped anddimensioned to closely receive fibers 31. At the end of the ferrulemounting process, each fiber is firmly held in position within itsrespective guide hole by epoxy, or other suitable material.

Prior to the fibers being bonded to the ferrule with epoxy, each fiberis rotated longitudinally with respect to the ferrule such that thecores of each fiber are aligned in a pre-determined orientation. Forinstance, each fiber could be oriented so one of its cores is in the 12o'clock position. The orientation could be performed manually or via anautomated process.

Ferrule 30 further comprises a pair of alignment holes 35. As discussedbelow, alignment holes 35 are configured to receiving respectivealignment pins in order to help align ferrule 30 as it is seated into amating structure.

It will be seen that by combining ferrule 30, containing appropriatelyaligned MCFs 31, with a suitably configured 2-dimensional VCSEL array,of the type shown in FIG. 2C (array 24), it is possible to realizeparallel transmission down 72 channels in the same space required for12-channel transmission with conventional single-core fibers. Since MTferrules are available with fewer holes, terminated variants with fewerfibers could also be produced. Also, multicore fibers could be utilizedin other multifiber connector configurations like MT-RJ and MPXconnectors, as previously mentioned. MT-RJ connectors typically contain2 to 4 fibers and MPX Connectors could be produced with 4, 8, or 12multicore fibers. In addition, multicore fibers with any number ofcores, and MT ferrules with any number of holes could be produced. Thus,multifiber connectors with various channel counts are possible.

For reliable connections between fibers, all of the fiber cores must bein contact, under pressure, when two multifiber connectors are mated.This is particularly important for multicore fibers, since the cores canbe located some distance from the axis of the fiber. When connectors arepolished, the endfaces of the fibers are convex. Thus, fiber-to-fibercontact pressure is required to deform (i.e., flatten) the convexendfaces enough to allow the outer cores to fully meet. Fiber-to-fibercontact between multifiber connectors is achieved by polishing themultifiber ferrules so the fibers protrude several micrometers, abovethe surface of the ferrule.

FIG. 4, discussed above, illustrates the protrusion of the MCFs 31 fromthe ferrule endface 34. As mentioned above, the MCFs have an outercladding diameter of approximately 125 μm. After assembly, each MCF willtypically protrude from the ferrule endface 34 a distance ranging from 1μm to 15 μm.

2. MULTICORE MULTIFIBER CONNECTORS USING D-SHAPED FIBERS

FIGS. 5 and 6 show perspective views of exemplary D-shaped 7-coremulticore fibers 50, 60 according to aspects of the invention. Eachmulticore fiber 50, 60 is provided with a flat side flat surface 52, 62extending along the length of the fiber. It should be noted thatalthough fibers 50 and 60 are each depicted with a single flat sidesurface, aspects of the present invention may also be practiced with afiber comprises a plurality of flat side surfaces.

In each multicore fiber 50, 60, the flat 52, 62 is strategically locatedto facilitate core orientation relative to the keying features of anoptical connector. In FIG. 5, the flat is adjacent to one of the MCFcores 54, so the position of that core, as well as that of the remainingcores can be oriented and fixed relative to the keying features of amultifiber connector. As shown in FIG. 6, the flat could be positionedadjacent to any two side-by-side cores 64, which would also allow theposition of those two cores, as well as that of the remaining cores, tobe oriented and fixed relative to the keying features of a connector.

3. Alignment Techniques for D-Shaped Multicore

A significant issue to be resolved in mounting a ferrule onto an end ofa multi-MCF cable is rotational alignment of the individual MCFs withinthe ferrule. It will be appreciate that when a multi-MCF cable end isstripped, and when the individual MCFs are loaded into a ferrule, therewill typically be some amount of rotational misalignment of the MCFcores. Thus, even if the individual MCFs are precisely aligned withinthe jacketed cable, and even if the ferrule guide holes precisely fitthe bare MCFs, it will typically still be necessary to perform aprecise, final rotational alignment before the individual MCFs areepoxied into their respective guide holes.

There are now described a number of structures and techniques thatprovide repeatable, cost-effective ways to achieve this precise, finalrotational alignment of individual multicore fibers within theirrespective ferrule guide holes. Examples of these structures andtechniques are described using D-shaped fiber 50, shown in FIG. 5, andferrule 30, shown in FIGS. 3 and 4. However, it will be appreciated thatthese examples are not intended to be limiting, and that it would bepossible to practice aspects of the invention, with suitablemodification as required, with different types of MCFs and ferrules.

FIG. 7 shows a cross section diagram of a D-shaped MCF 50, which hasseven cores 54, and a flat side surface 52 proximate to one of the cores54. MCF 50 is loaded into a circular ferrule guide hole 70, similar toferrule guide holes 40 shown in FIG. 4. It will be seen that althoughthere is a small gap 71 between the fiber's flat side surface 52 and theperimeter of guide hole 70, the guide hole 70 nonetheless providesradial confinement of fiber 50 in all directions.

According to the below-described aspects of the invention, the MCF flatside surface 52 is used to achieve a precise rotational alignment of MCF50 within circular guide hole 70.

FIG. 8 shows a perspective view of ferrule 30, into which there has beenloaded a multi-MCF cable 80 containing a plurality of individual MCFs50. For the purposes of the present description, it is assumed that MCFs50 are arranged within cable 80 in a side-to-side linear array, andthat, within cable 80, the MCFs have a desired rotational alignment, ora substantial approximation thereof, in which the flat side surfaces 52of all of the fibers 50 are lined up with each other across the array,and all face in the same direction. It should be noted, however, thataspects of the invention may also be practiced with other types ofalignment schemes, including schemes in which the respective flat sidesurfaces of some or all of the individual fibers do not line up witheach other.

An end of cable 80 is prepared for connectorization by stripping awaythe jacket and other protective layers to expose the bare fibers 50. Asshown in FIG. 8, the cable is then loaded into ferrule 30, with acertain amount of excess fiber 50 extending out of the ferrule endface.The length of the excess fiber will be dictated by the requirements ofthe particular alignment technique used.

FIG. 9 is a diagram illustrating a general technique for providing theabove-described final alignment of fibers 50 within their respectiveferrule guide holes. According to various aspects of the inventiondiscussed below, ferrule 30 and cable 80 are loaded into an alignmentfixture having an alignment surface 90 therein. The alignment surfaceincludes structures for causing the flat side surfaces of the individualfibers 50 to lie flat against the alignment surface 90, thereby causingthe individual fibers to be rotationally aligned within their respectiveguide holes.

Once the final rotational alignment has been performed, epoxy or othersuitable material can be injected into the guide holes to hold thefibers in place. The excess fiber can then be trimmed proximate to theferrule endface, and the trimmed ends can then be polished to producethe desired convex shape for the fiber endfaces.

Four alignment techniques are described: (1) the “ramp” technique; (2)the “tapered slot” technique; (3) the “side-entry slot” technique; and(4) the “wedge” technique. Each technique is described in turn below.

3.1 Ramp Technique

FIGS. 10A-10B shows a perspective view of an alignment fixture 100employing a “ramp” technique, in accordance with an aspect of theinvention. Alignment fixture 100 comprises an L-shaped chassis 101having a base 102, an upright 103, and a ramp 104. The upper surface ofbase 102 includes a cutout 105 therein. A pair of MT alignment pins 106extends from the upright 103, substantially parallel with the uppersurface of base 102. Ramp 104 is positioned between the pair of MTalignment pins 106, and provides a smooth transition from a lower frontelevation to a higher rear elevation.

Ferrule 30, with protruding fibers 50, is loaded into alignment fixture100 by positioning the ferrule 30 such that front bottom edge of ferrulehead 33 abuts the upper surface of base 102, such that the front bottomedge of ferrule base 32 abuts the front portion of cutout 105, such thatthe ferrule alignment holes 35 are aligned with alignment pins 106, andsuch that the exposed ends of bare fiber 50 abut, or are proximate to,the upper surface of ramp 104.

In. FIG. 10A, ferrule 30 has been loaded into fixture 100, but fibers 50have not yet come into contact with ramp 104.

The ferrule 30 is then advanced towards fixture upright 103. Therespective shapes of the cutout 105 and the ferrule base 32, and theclose fit therebetween, causes the ferrule to be guided along asubstantially straight line, whereby alignment pins 106 become seated inholes 35. The movement of the ferrule causes the fiber ends to be urgedagainst the ramp surface. The urging of the fiber ends against the rampsurface causes the fiber flats to become aligned with respect to theramp surface.

In FIG. 10B, ferrule 30 has been advanced toward fixture upright 103 asufficient distance to cause fibers 50 to come into contact with ramp104.

The operation of fixture 100 is illustrated in FIGS. 11A-D. For thepurposes of illustration, the amount of rotational alignment has beenexaggerated. In actual use, the amount of alignment will besignificantly less.

In FIG. 11A, fiber 50 has not yet made contact with ramp 104.

In FIG. 11B, fiber 50 has come into contact with ramp 104.

In FIG. 11C, fiber 50 has traveled far enough up ramp 104 to cause apartial rotational alignment of fiber 50.

In FIG. 11D, fiber 50 has traveled far enough up ramp 104 to causecomplete rotational alignment of fiber 50.

It will be appreciated that the depicted structures may be modified bythe inclusion of additional, or different, alignment and retentionstructures and may be practiced using differently shaped fibers andramps.

3.2 Tapered Slot Technique

FIGS. 12A-12C show perspective views of an alignment fixture 120employing a “tapered slot” technique according to a further aspect ofthe invention. (FIG. 12B shows a wireframe version of FIG. 12A.)

Alignment fixture 120 comprises an L-shaped chassis 121 having a base122 and an upright 123. The upper surface of base 122 includes a cutout124 therein. Upright 123 includes a tapered slot 125 generally alignedwith exposed fibers 50. A pair of MT alignment pins 126 extends from theupright 123, substantially parallel with the upper surface of base 122.Tapered slot 125 is positioned between the pair of MT alignment pins126.

Ferrule 30, with protruding fibers 50, is loaded into alignment fixture120 by positioning the ferrule 30 such that front bottom edge of ferrulehead 33 abuts the upper surface of base 122, such that the front bottomedge of ferrule base 32 abuts the front portion of cutout 124, such thatthe ferrule alignment holes 35 are aligned with alignment pins 126, andsuch that the exposed ends of bare fiber 50 are generally aligned withtapered slot 125.

In FIGS. 12A and 12B, ferrule 30 has been loaded into fixture 120, butfibers 50 have not yet been seated in tapered slot 125.

The ferrule 30 is then advanced towards fixture upright 123. Therespective shapes of the cutout 124 and the ferrule base 32, and theclose fit therebetween, causes the ferrule to be guided along asubstantially straight line, whereby alignment pins 126 become seated inholes 35. The movement of the ferrule causes the fiber ends to be urgedinto tapered slot 125.

In FIG. 12C, ferrule 30 has been advanced toward fixture upright 123 asufficient distance to cause fibers 50 to be fully seated in taperedslot 125.

The front side of the slot has a height that is larger than the diameterof the D-shaped fiber (i.e., greater than 125 μm). The back side of thetapered slot has a height smaller than the fiber O.D. (i.e., less than125 μm), but barely large enough to allow the D-Shaped fiber to passthrough, when the flat is parallel to the slot. Therefore, when theD-shaped fibers are pushed into the slot, the slot will cause the flatsof the D-shaped fibers to align horizontally.

FIGS. 13A and 13B are a pair of diagrams illustrating the operation ofthe tapered slot technique.

In FIG. 13A, non-aligned fiber 50 only fits part way into tapered slot125. Urging of fiber 50 deeper into slot 105 causes the fiber 50 torotate in order to allow it to fit into the narrowed slot.

In FIG. 13B, the fiber 50 has been fully seated into slot 125.

It will be appreciated that the depicted structures may be modified bythe inclusion of additional, or different, alignment and retentionstructures and may be practiced using differently shaped fibers andslots.

3.3 Side-Entry Slot Technique

FIGS. 14A and 14B are perspective views of an alignment fixture 140employing a “side-entry slot” technique, according to a further aspectof the invention. Fixture 140 comprises an L-shaped chassis 141 having abase 142 and an upright 143. The upper surface of base 142 includes acutout 144 therein. Upright 143 includes a side-entry slot 145 that issubstantially parallel to the upper surface of base 142, at a heightaligned with the exposed fibers 50 protruding from the endface offerrule 30.

The ferrule 30, with roughly aligned protruding fibers 50, is loadedinto fixture 140 by positioning the ferrule 30 such that the left bottomedge of the ferrule head 33 abuts the upper surface of fixture base 142,such that the left bottom edge of ferrule base 31 is seated in cutout144, and such that the exposed fibers 50 are in alignment withside-entry slot 145.

Ferrule 30 is advanced in a right-to-left direction. The roughly alignedmulticore fibers 50, protruding out of the ferrule endface, are pushedlaterally into slot 145. The slot has a height smaller than the fiberouter diameter (i.e., less than 125 μm), but barely large enough toallow the D-Shaped fibers to enter, when the fiber's flat side surfaceis parallel with the upper and lower surfaces of slot 145. Therefore,when the D-shaped fibers are pushed into the slot, the slot will causethe flats of the D-shaped fibers to align horizontally.

In FIG. 14A, ferrule 30 has been loaded into fixture 140, but protrudingfibers 50 have not yet entered slot 145.

In FIG. 14B, ferrule 30 has been advanced far enough into fixture 140that all of the protruding fibers 50 have been pushed into the narrowestsection of the side-entry slot, resulting in the rotational alignment ofthe fibers within their respective ferrule guide holes.

FIG. 15 shows a diagram, illustrating the operation of the side-entryslot. As shown in FIG. 15, the lateral movement of fibers 50 into thenarrowest section of the slot causes the fibers to be rotated into theorientation required to fit between the upper and lower slot surfaces.

It will be appreciated that the depicted structures may be modified bythe inclusion of additional, or different, alignment and retentionstructures and may be practiced using differently shaped fibers andslots.

3.4 Wedge Technique

FIGS. 16A and 16B show perspective views of an alignment fixture 160employing a “wedge” technique, according to a further aspect of theinvention. Fixture 160 comprises an L-shaped chassis 161 having a base162 and an upright 163. The upper surface of base 162 includes a cutout164 therein. Upright 163 includes a cavity 165 with an inner surfacecomprising a pedestal 166 that is substantially parallel to the uppersurface of base 162, and substantially in alignment with protrudingfibers 50. Upright 163 further includes first and second alignment pins167 at the left and right sides of pedestal 166.

As shown in FIG. 16A, the ferrule 30, with roughly aligned protrudingfibers 50, is loaded into fixture 160 by positioning the ferrule 30 suchthe bottom face of the ferrule base 32 is seated in cutout 164, suchthat the alignment pins 167 are seated in ferrule holes 35, and suchthat the front end of the protruding fibers 50 are positioned on top ofpedestal 166.

As shown in FIG. 16B, a wedge 168 is inserted into the mouth of cavity165. The wedge 168 is shaped to fit closely into cavity 165. Thus,pushing wedge 168 into position within cavity 165 places a downward loadon the fibers, which causes the flats to align horizontally.

FIGS. 17A-17C are a series of diagrams illustrating the operation ofalignment fixture 160.

In FIG. 17A, the wedge has been inserted, but has not yet started topress down on fibers 50.

In FIG. 17B, the wedge has been partially inserted, causing a partialrotational alignment of the fibers 50.

In FIG. 17C, the wedge has been inserted to a depth sufficient to causecomplete rotational alignment of the fibers 50.

Here again, other structures incorporating different ferrule retentionfeatures are also feasible. Also, spring or clip mechanisms could beused as alternate methods to apply the downward force to the fibers.

4. MULTIFIBER FERRULES WITH D-SHAPED HOLES AND D-SHAPED FIBERS

According to a further aspect of the invention, the issue of providingprecise rotational alignment of multicore fibers is addressed byproducing special multifiber MT ferrules with D-shaped holes,pre-aligned in the desired orientation. These ferrules could befabricated, for example, using a suitable injection-molding ortransfer-molding technique. These special MT ferrules can be fabricatedfrom glass-filled PPS, thermoset epoxy, or any other suitable thermosetor thermoplastic polymer.

FIG. 18 shows a close-up view an endface of an MT ferrule endface withpre-aligned D-shaped holes 181. In this approach, a D-shaped fiber isautomatically aligned, upon insertion into the D-shaped holes 181 of theMT ferrule 180, since the fiber flat side surface has to be in line withthe hole's corresponding flat side surface 182 in order to facilitatefiber insertion.

FIG. 19 is a close-up front view of the ferrule endface with insertedD-shaped fibers 50.

The depicted ferrule 180 can be modified for use with various otherfiber orientations. For example, flat side surfaces on different fibers,in the same ferrule, could be facing different directions. Also, fibersand ferrule holes with two opposing flat surfaces (such as a “double D”configuration) could be used.

5. MULTICORE MULTIFIBER CONNECTORS USING POLYGONAL FIBERS

While D-shaped fibers will facilitate fiber alignment, alternate fibergeometries that would provide, to varying degrees, similar functionalityare feasible. For instance, fibers with polygonal cross sections couldalso be employed. The flat surfaces of the polygonal fibers would helpfacilitate core alignment. For instance, square, rectangular,triangular, pentagonal, hexagonal, octagonal, etc., fibers could beused.

FIG. 20 shows perspective views of a square fiber 200 and a hexagonalfiber 201. Also, special multifiber MT ferrules with polygonal holescould be molded to accommodate and align specific polygonal fibers.

6. MULTICORE MULTIFIBER CONNECTORS USING OTHER FIBER SHAPES

In addition to the fiber geometries already mention (i.e. circular(elliptical), D-shaped, and polygonal), other fiber geometries thatwould provide, to varying degrees, similar functionality are feasible.For instance, fibers with irregular cross sections (i.e. a combinationof curved and flat surfaces) could also be employed. The symmetry orflat surfaces of the fibers would help facilitate core alignment. Hereagain, special multifiber MT ferrules with irregular holes could bemolded to accommodate and align specific fiber geometries.

7. GENERAL TECHNIQUES

FIGS. 21 and 22 show flowcharts of general techniques 210, 220,according to aspects of the invention. It should be noted that FIGS. 21and 22 are intended to be exemplary, rather than limiting. The presentinvention may be practiced in a number of different ways, usingdifferent combinations of some or all of the elements set forth in thesedrawings, as well as combinations including elements not explicitly setforth in these drawings.

FIG. 21 shows a flowchart of a general technique 210, according toaspects of the invention, for aligning multicore fibers within amultifiber ferrule.

General technique 210 comprises the following steps:

211: Strip an end portion of a multicore fiber cable containing aplurality of multicore fibers, so as to expose the bare multicorefibers.

212: Insert the exposed multicore fibers into a plurality of guide holesdefined longitudinally through a ferrule subassembly.

213: Align the cores of the fibers rotationally, in a predeterminedorientation, relative to the ferrule.

214: Bond the multicore fiber within the ferrule.

215: Trim the fiber at a ferrule endface so as to create a plurality ofmulticore fiber endfaces protruding from the ferrule endface.

216: Polish the multicore fiber endfaces.

FIG. 21 shows a flowchart of a further general technique 210, accordingto aspects of the invention, for aligning multicore fibers within amultifiber ferrule.

221: Strip an end portion of a multicore fiber cable containing aplurality of multicore fibers, so as to expose the bare optical fibers.

222: Insert the exposed multicore fibers into a plurality of guide holesdefined longitudinally through a ferrule subassembly.

223: Bond the multicore fibers within the ferrule.

224: Trim the multicore fibers at a ferrule endface, so as to create aplurality of multicore fiber endfaces protruding from the ferruleendface.

225: Polish the multicore fiber endfaces.

8. CONCLUSION

While the foregoing description includes details which will enable thoseskilled in the art to practice the invention, it should be recognizedthat the description is illustrative in nature and that manymodifications and variations thereof will be apparent to those skilledin the art having the benefit of these teachings. It is accordinglyintended that the invention herein be defined solely by the claimsappended hereto and that the claims be interpreted as broadly aspermitted by the prior art.

1. A method for aligning multicore fibers within a multifiber ferrule,comprising: (a) stripping an end portion of a multicore fiber cablecontaining a plurality of multicore fibers, so as to expose the baremulticore fibers; (b) inserting the exposed multicore fibers into aplurality of guide holes defined longitudinally through a ferrulesubassembly; (c) aligning the cores of the fibers rotationally, in apredetermined orientation, relative to the ferrule; (d) bonding themulticore fiber within the ferrule; (e) trimming the fiber at a ferruleendface so as to create a plurality of multicore fiber endfacesprotruding from the ferrule endface; and (f) polishing the multicorefiber endfaces.
 2. The method of claim 1, wherein the multicore fibershave a circular profile.
 3. The method of claim 1, wherein the multicorefibers have at least one flat side surface identifying a particularrotational orientation of the plurality of cores.
 4. The method of claim3, wherein the multicore fibers have a D-shaped profile.
 5. The methodof claim 3, wherein the multicore fibers have a double D-shaped profile.6. The method of claim 3, wherein the multicore fibers have a polygonalprofile.
 7. The method of claim 3, wherein step (c) includes aligningthe multicore fibers using a fixture that urges the flat side surfacesof the multicore fibers against a fiber alignment surface, so as tocause each of the multicore fibers to be rotationally aligned within itsrespective guide hole.
 8. A method for aligning multicore fibers withina multifiber ferrule, comprising: stripping an end portion of amulticore fiber cable containing a plurality of multicore fibers, so asto expose the bare optical fibers; inserting the exposed multicorefibers into a plurality of guide holes defined longitudinally through aferrule subassembly; bonding the multicore fibers within the ferrule;trimming the multicore fibers at a ferrule endface, so as to create aplurality of multicore fiber endfaces protruding from the ferruleendface; and polishing the multicore fiber endfaces.
 9. The method ofclaim 8, wherein the plurality of multicore fibers includes at least onemulticore fiber having at least one flat side surface identifying aparticular rotational orientation of the plurality of cores.
 10. Themethod of claim 9, wherein the plurality of guide holes includes atleast one guide hole having a shape including a flat side surfacecorresponding to the at least one flat side surface of the multicorefibers, such that alignment of the at least one flat side surface ofeach multicore fiber against the corresponding flat surface within itsrespective guide hole results in a rotational alignment of the pluralityof cores.
 11. A method according to claim 10, wherein the at least onemulticore fiber and the at least one guide hole having flat sidesurfaces have a D-shaped profile.
 12. A method according to claim 10,wherein the at least one multicore fiber and the at least one guide holehaving flat side surfaces have a double D-shaped profile.
 13. A methodaccording to claim 10, wherein the at least one multicore fiber and theat least one guide hole having flat side surfaces have a polygonalprofile.